Marine riser pull-down device



June 30, 1970 w. H.` PETERSEN MARINE RISER PULL-DOWN DEVICE 2 Sheets-Sheet l Filed May 23, 1968 INVENTORI WILLIAM H. PETERSEN BVI/,wgvfe/ ms ATTORNEY` FIG.

June 30, 1970 w. H. PETERsr-:N

x MARINE RISER PULL-DOWN DEVICE B Sheets-Shet 2 Filed May 23, 1968 amv INVENTORI WILLIAM H. `jPETERsEN BY: i

Hls ATTORNEY United States Patent O 3,517,737 MARINE RISER PULL-DOWN DEVICE William H. Petersen, Houston, Tex., assignor to Shell Oil Company, New York, N.Y., a corporation of Delaware Filed May 23, 1968, Ser. No. 731,495 Int. Cl. E21h 7/12; E21c 19/00 U.S. Cl. 166-.6 2 Claims ABSTRACT OF THE DISCLOSURE This invention relates to apparatus for use in carrying out operations with respect to underwater wells at deep water locations from a floating vessel. More particularly, the present invention pertains to apparatus associated with a wellhead connector depending from a floating vessel, said apparatus being effective to attach said connector to a cooperating member comprising a portion of an underwater wellhead structure, thereby establishing communication between said structure and said vessel.

In an attempt to locate new oil fields, an increasing amount of well drilling has been conducted at ofshore locations, such for example, as off the coasts of California, Louisiana and Texas. As a general rule, the strings of casing in a well, together with the tubing strings or string, extend to a point above the surface of the water where they are closed in a conventional manner that is used with respect to onshore wells, with a conventional wellhead assembly being attached to the top of the casing. Such arrangements constitute a hazard to navigation and recently, methods and apparatus have been developed for drilling and completing wells wherein both the well casinghead, and subsequently the wellhead assembly and casing closure device, are located underwater at depths suicient to allow ships to pass over them. Underwater structures of this type are, of course, exposed to conditions such as the corrosive nature of sea water and the presence of marine life which tends to grow and become encrusted on metallic structures below the surface of the water.

Since it is necessary from time to time to go back into a well wherever it has been completed for servicing or workover operations, it is desirable to have an underwater wellhead structure of suitable design so that communication may be had with the interior of the well itself or, alternatively, so that at least a portion of the structure may be removed to the surface of the water for maintenance operations. An underwater arrangement of this sort is shown and described in U.S. Pat. No. 3,064,735 issued Nov. 20, 1962, to R. J. Bauer et al.

Since the depths at which such underwater structures are often placed are of such magnitude as to preclude use of divers, a number of approaches have been devised for remotely establishing communication between these underwater structures and vessels floating on the surface of a body of water so that the desired workover operations may be carried out. One technique that has found considerable acceptance is that of lowering a wellhead connector by means of a pipe string or marine conductor pipe from the vessel into locking engagement with the underwater wellhead assembly. Tubing members may be disposed with the marine conductor pipe to cooperate with similar members within the assembly and/or well casing so that the various operations may be carried 3,517,737 Patented June 30, 1970 "ice out. Copending U.S. application Ser. No. 731,31, led May 23, 1968, discloses one suitable marine conductor pipe-wellhead connector arrangement that may be utilized when carrying out operations of the above-described nature.

One of the problems encounteerd when remotely attaching a wellhead connector to an underwater structure is that not only must such operation be carried out from a vessel several hundreds of feet above but, in addition, the up and down movement of the floating vessel and the marine conductor pipe depending therefrom makes it difficult to control the positioning of the pipe and connector with respect to the fixed wellhead structure. For example, a sudden drop of the floating vessel due to wave or other surface activity of the water during the connecting operation may result in buckling of the marine conductor pipe or damage to the underwater structure or connector.

A method and apparatus for overcoming this diiculty are disclosed in copending U.S. application Ser. No. 732,916, led May 29, 1968, whereby a controlled remote connection may be made between an underwater wellhead structure and a marine conductor assembly, including a connector and a marine conductor pipe, depending from a floating vessel, regardless of the degree of up and down motion of the vessel. In said last mentioned U.S. application an arrangement of lines and pulleys is disclosed to enable an operator on board a vessel to effect the pull down of the marine conductor assembly in opposition to a substantially constant upwardly directed force until an initial engagement is made between a portion of the marine conductor assembly and a mono-post of an underwater wellhead structure. After the portion has been latched to the mono-post the same arrangement of lines and pulleys is used to effect `final attachment between the connector and the landing mandrel or entry conduit of the underwater wellhead structure.

While the approach described in said U.S. patent application Ser. No. 732,916 is satisfactory in most instances, there are situations when even greater control may be desired when effecting the engagement between a connector and a cooperating member, such as a landing mandrel, on the underwater wellhead structure. For example, specialized design features or instrumentation of a particularly delicate nature and associated with the connector or other portions of the marine conductor assembly may require additional control in the connecting operation to avoid damage during that operation.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide apparatus whereby a great degree of control may be' exercised by the operator when eifecting attachment between a wellhead connector and a landing mandrel comprising a portion of an underwater wellhead structure.

This object has been attained in the present invention by providing a marine conductor adapted to be yieldably supported by a oating platform, said conductor having attached to the lower end thereof wellhead connector means adapted to cooperatively engage mandrel means on an underwater wellhead assembly. A pull-down apparatus including prime mover means is fixedly positioned with respect to the wellhead connector means. Downward movement of the pull-down apparatus over upstanding post means associated with the wellhead assembly serves to lock these two elements into engagement. Actuation of the prime mover means is then effective to pull the wellhead connector means down into engagement with said mandrel means against the upward force exerted by said yieldable support means.

3 DESCRIPTION OF THE DRAWING This and other objects of the subject invention will be understood from the following description takenwith Vreference to the accompanying drawings wherein:

FIG. 1 is a diagrammatic view taken in longitudinal projection illustrating the lower portion of a floating vessel having depending therefrom a marine conductor assembly prior to its operative engagement with an underwater wellhead structure; i

FIG. 2 is a diagrammatic longitudinal view in partial cross-section illustrating the relative positions assumed by elements of the apparatus according to the present invention and the marine conductor assembly associated therewith after initial engagement has been made with the underwater wellhead structure and prior to iinal pull down of the connector into operative engagement with the landing mandrel of the wellhead structure; and

FIG. 3 is a diagrammatic, longitudinal view in partial cross-section illustrating the relative positions assumed by elements of the apparatus according to the present invention and the marine conductor assembly associated therewith after final pull down of the connector into operative engagement with the landing mandrel of the wellhead structure.

Referring to FIG. 1 of the drawing, a platform or barge 11 of any suitable fioatable type is illustrated as floating on the surface of a body of water 12 and positioned over a preselected well site by suitable barge positioning means or by being anchored to the sea bed 13 by suitable anchors (not shown) connected to anchor lines 14 and 15. Equipment of this type may be used when carrying on well workover operations in water depths varying from about 100 to 1,500 feet or more. The vessel is equipped with a conventional derrick 16 as well as other usual auxiliary equipment needed during workover operations relating to a well such as a rotary table 17, a hoist system (not shown), etc. The derrick 16 is preferably, but not necessarily, positioned on an elevated rig floor or operating platform 18 which is supported by means of a framework 19 over slot or well 20. When using the apparatus according to the present invention, the slot 20 may be either centrally located or extend in from one edge. However, operations may be 'carried out over the side of the barge or vessel without the use of a slot as from a portion of the operating platform extending out over one end of the remainder of the vessel.

An underwater wellhead structure, generally represented by numeral 21 in FIG. 1, is illustrated as comprising a base member 22 which is positioned on sea bed 13 and lixedly secured to conductor pipe or large diameter well casing 23 which extends down into a well which has been previously drilled, and is preferably cemented therein. A pair of vertically-extending guide columns 24 and 25 are axed to base member 22 for the purpose which will be more fully lbrought out below. Disposed Ibetween guide columns 24 and 25 is a production wellhead assembly 26 which is of conventional design. Although illustrated herein in somewhat schematic fashion, it may be assumed that the disclosed assembly is of the general type shown in the above-mentioned U.S. Pat. No. 3,064,735, issued Nov. 20, 1962, to R. I. Bauer et al. The assembly includes at least one production ow line 26a which is connected by suitable coupling means to underwater pipeline 26b. Assembly 26 is maintained in operative communication with well casing 23 by means of a conventional wellhead connector unit 27. An elongated landing mandrel or entry conduit 28 is ixedly secured at its lower end to the body portion of the remainder of assembly 26. Production wellhead assembly 26 differs from that disclosed in U.S. Pat. No. 3,064,735 in that entry conduit or landing mandrel 28 has extending therefrom in an offset manner a bracket member 29 with a mono-post 30 affixed thereto and extending vertically therefrom.

A single guide cable 31 is affixed to the end of monopost 30 and extends upwardly to vessel 11. The guide cable 31 may be permanently attached to mono-post 30 or may Ibe secured thereto by suitable latch means which has been previously remotely brought into engagement with the mono-post by means of suitable apparatus manipulated from vessel 11. One suitable apparatus for performing this is disclosed in copending U.S. patent application Ser. No. 749,171, filed July 31, 1968. In this last-mentioned application, a specially designed tool incorporating wellhead assembly locating and positioning means, such as a TV camera and/ or a sonar unit, is lowered by means of a pipe string from a floating vessel onto the assembly to attach a latching element and cable or guide line to a mono-post. As previously stated, however, the cable may be permanently attached to the mono-post with grappling hooks or other means being employed to initially establish a connection between the free end of the cable and the vessel.

At its uppermost extent, the cable or mono-guideline 31 passes over sheave 32 on board vessel 11 and thence to a hoist 33 of any known design which is iixedly secured to deck member 34. Sheave 32 is rotatably mounted on arm 35 which in turn is operatively associated for reciprocal movement with tensioner device 36 of any known type which is aixed to operating platform 18. It should be pointed out at this juncture that the arrangement on board vessel 11 which is described in this paragraph and the following paragraph is disclosed more fully in copending U.S. patent application Ser. No'. 732,916, filed May 29, 1968, and forms no part of the subject invention of the instant application. Accordingly, in the interest of brevity and simplicity, the operation thereof will be described only insofar as it is necessary for proper understanding of the subject invention.

A power winch 37 is also xedly secured to deck member 34 and has operatively associated therewith a pulldown line or cable 38. From winch 37 pull-down line 38 passes over pulley or sheave 39 rotatably mounted on arm 35 in ganged fixed relationship with respect to pulley 32. Pull-down line 38, after passing over pulley 39, proceeds downwardly and under a still additionally pulley 40 which is mounted for rotatable movement at a preselected location on mono-guideline 31 by any suitable means, such as a hydraulic clamp member 41. Pull-down line 38 is then connected at its end to a marine riser or marine conductor 42 which depends from vessel 11 and is biased in an upward direction under a substantially constant predetermined force by means of a hydraulic tensioner 43 of any known type.

As previously stated, the apparatus described in the above last two paragraphs is disclosed more fully in copending U.S. patent application Ser. No. 732,916, filed May 29, 1968. For purposes of understanding the operation of the invention which is the subject of the instant application, it needs only to be understood that said apparatus serves as a motion cancellation means by maintaining a substantially fixed distance between the marine conductor 42 and wellhead assembly 26 regardless of the degree of up and down motion imparted to vessel 11 by wave or other wave surface action. By actuating power hoist 37, line 38 serves to pull marine conductor 42 in a downward direction in a controlled manner.

Disposed at the lower end of marine conductor 42 is a wellhead connector 43 of any desired type and construction. The connector is of a size and having a bore to fit telescopically onto and to make sealing engagement with landing mandrel 28 of wellhead assembly 26. If desired, guideline connector means may be frame mounted on the connector 43 to establish guidelines 44 and 45 be- -tween the vessel 11 and the underwater wellhead structure 21. The guideline connector means forms no part of the present invention but is shown here for purposes of illustration only. Quite briefly, the form shown comprises cylindrical housing members 46 and 47 in which latch connector members 48 and `49, respectively, are freely and 49, against the respective bottoms of cylindrical housing members 46 and 47. It is Vto be understood that upon release of the force imparted by the constant tension hoists 50 and 51, Ylatch connector members 48 and49 will be free to drop downwardly through the cylindrical housing members. The particular arrangement shown here is more fully disclosed in copending U.S. patent application Ser. No. 731,382, filed May 23, 1968. As stated above, however, the guideline or cable connecting means forms no part of the present invention.

As may be seen with particular reference to FIGS. 2 and 3, a pull-down apparatus, indicated generally by reference numeral `60, is affixed at its lower end to wellhead connector 43 by previously referred to frame 43b. The pull-down apparatus includes a lower tubular portion 61 having a ilange 62 and an upper tubular portion 63. Upper tubular portion has a ange 64 which is affixed by any known fastening means, such as bolts (not shown) to ange 62, thereby serving to concentrically align tubular portions 61 and 63 and maintain them in a -fixed endto-end relationship to one another. To provide additional stability to the pull-down apparatus 60, upper tubular portion 63 may be connected by means of a bracket member 65 to a lower portion of marine conductor 42. Welded or otherwise attached to the top-most end of upper tubular portion 63 is an end plate 66 having a centrally located circular throughbore 67 therein. The opposite end of upper tubular portion 63, i.e. the lowermost end as viewed in FIGS. 2 and 3, is also partially closed by an inwardly extending wall 68 defining a throughbore 69 of a size corresponding to that of throughbore 67.

Disposed within both tubular portions 61 and 63 and passing through each of the thoughbores l67 and 69 is a hollow cylindrical element 70 which has aiiixed thereto a piston member 71. Piston member 71 engages the inner wall of upper tubular portion 63 in a fluid-tight manner while at the same time being of a dimension permitting longitudinal movement therein. Seal members are preferably provided about throughbores 67 and 69, as well as around the periphery of piston member 71, to ensure, a liquid-tight seal with their respective mating elements. Cylindrical element 70 terminates at its lowermost end with an integrally attached housing 72 which s also of cylindrical configuration with an external diameter slightly less than that of the inner wall of lower tubular portion 61. As shown in hidden lines in FIGS. 2 and 3, the interior of housing 72 forms a cavity 73 having a configuration corresponding to the top portion of mono-post 30. A latch 74 is mounted on housing 72 and has a locking element 75 which is selectively movable in or out of cavity 73. In the illustrated embodiment, latch 74 is of a simple hydraulic type with line 76 leading to any desired source of hydraulic uid. It should be understood, however, that any manner or type of latch, such as one electrically activated, may be used to equal advantage. Line 76 and a portion of latch 74 pass through a longitudinal slot in the side of lower tubular portion 61. It should be noted at this point that additional hydraulic lines 77 and 78 communicate with the interior of upper tubular portion 63 with line 77 positioned above piston member 71 and line 78 being positioned below. As with line 76, hydraulic lines 77 and 78 communicate with a suitable source of hydraulic uid under pressure (not shown) preferably on board vessel 11.

The operation of the device according to the present invention will now be described. As stated above, monoguideline 31 has been attached previously to mono-post 30 and extends upwardly to vessel 11. At the vessel, mono-guideline 31 is threaded through hollow cylindrical element 70 and the wellhead connector 43 `and apparatus depending therefrom, including pull-down apparatus 60, are lowered from the vessel by lengthening marine conductor 42 in the usual manner, i.e. through the addition of individual conductor pipe sections to the string. This lowering operation is continued, with hollow cylindrical element 70 serving to guide the descent alongmonoguideline 31, until the bottom end of lower tubular portion =61 is positioned a fixed predetermined distance over mono-post 30. After this stage of the lowering operation has been reached, the upper portion of marine conductor 42 is attached to tensioner 43 and the motion cancellation and pull-down arrangement on board vessel 11 is set up as shown in FIG. 1 and as is more fully disclosed in copending U.S. patent application Ser. No. 732,916, filed May 29, 1968. Winch 37 is then actuated and pulldown line or cable 38 serves to place housing 72 onto mono-post 30 as shown in FIG. 2. It should be noted that during at least the final stages of the abovedescribed lowering operation, hydraulic line 77 is pressured up, thereby continuously urging piston member 71, cylindrical element 70 and housing 72 in a downward direction. After the upper portion of mono-post 30 has seated within cavity 73 of housing 72, latch 74 is actuated by pressuring up line 76 thereby bringing locking element 75 into engagement with a cooperating indent on the mono-post as shown in FIG. 2. In this manner, housing 72 is positively locked to mono-post 30.

Final pull-down of wellhead connector 43 into engagement with landing mandrel 28 is effected by actuating suitable valves (not shown) in hydraulic lines 77 and 78 to relieve the pressure above piston member 71 within upper tubular portion 63 and introduce pressurized fluid through line 78 into the space defined by the inner wall of tubular portion 63, inwardly extending wall 68 and the bottom of piston member 71.

Since housing 72 is locked to mono-post 30, application of hydraulic pressure through line 78 causes tubular portions 61 and `63, and hence marine conductor 42 and wellhead connector 43 to be pulled downwardly against the upwardly directed force being applied thereto by hydraulic tensioner 43 on board vessel 11. Through careful adjustment and maintenance of the pressure being applied through line 78 precise control of the rate of pull-down may be had in those situations where such degree of control is necessary. At the end of this nal pulldown operation, the elements of the device according to the present invention are in the positions illustrated in FIG. 3 wherein the wellhead connector 43 is positioned directly on the landing mandrel 28. It is to be assumed, of course, that the wellhead connector, as is customary, includes one or more passageways which establish fluid communication between the interior of the well and either the interior of the marine conductor 42 itself o1' tubing strings, such as those designated by reference numerals 80 and 81, disposed within the conductor and extending to the vessel.

To ensure proper positioning of the connector 43 with respect to landing mandrel 28 prior to engagement therebetween, it is desirable, but not absolutely necessary, to provide some form of aligning means. In the illustrated embodiment, such an alignment means is in the form of a pin and slot arrangement, with a fixed pin 82 being positioned near the bottom of lower tubular portion 61 to cooperate with a shoulder 83 on mono-post 30 as the tubular portion 61 is lowered thereover upon application of pressurized hydraulic lluid through line 78. In this manner, connector 43 is placed in alignment with landing mandrel 28 during initial stages of the tinal pulldown.

7 I claim as my-invention: 1. lIn combination: a marine conductor vadapted to be yieldably supported by operational platform means floating on the surface of a vbody of water; l wellhead assembly positioned below the surface of the Water and in operative communication with a well extending into the earth below 'said body of water, said wellhead assembly including upstanding post means and mandrel means; wellhead connector means attached to said marine conductor at the lower end of the'conductor and adapted to cooperatively engage said mandrel means; pull-down apparatus including Vprime mover means xedly positioned with respect to said wellhead connector means;

latch means on said pull-down apparatus adapted to eifect locking engagement between said post means and said pull-down apparatus; and said pull-down apparatus after having been placed into locking engagement with said post means being elec- 'References Cited UNITED STATES PATENTSv t, y 11/1962,v Hayes f s 166-.5 4/1965 Goepfert -175--7 X 2/1966 Postlewaite 175-7 t 4/,1967 Crain v v 1616-,5 2/1968l .Posrlewaite 166-.6

NILE C. BYERS, sr., Primary Examiner R.` E. FAVREAU, Assistant Examiner' 

